1. Field of the Invention
The present invention relates to an electronic ignition system for an engine, and more particularly to an electronic ignition that prevents deleterious wearing of the conventional ignition breaker-points while utilizing these points to actuate spark generation.
2. Description of the Prior Art
In a conventional ignition system for an automotive or marine engine, high current from the battery is intermittently switched to the primary of the ignition coil by closure of a set of breaker points normally mounted in the distributor. As the breaker points open, the collapsing magnetic field in the ignition coil primary induces a high voltage in the secondary. This voltage is distributed to the engine plugs by the distributor and used to create the spark that ignites the fuel mixture. Although this system has been employed successfully for many years, it suffers the inherent shortcoming that the points gradually are worn away as a result of the high-current arcing. Such arcing causes metal transfer across the points, oxidation and erosion. Point lifetime is reduced, and there is a slight but continuous change in ignition timing over the life of the points. Eventually, this causes misfiring.
Electronic ignition systems offer the advantage of eliminating such problems associated with point wear. In prior art electronic ignition systems, the points often were eliminated completely, and some alternative timing device, physically connected to the engine or distributor, was used to actuate the ignition system. For example, optical or magnetic switching devices have been used in place of the cam and breaker points. In a typical device of this type, a toothed-wheel called a "reluctor" is attached to the distributor shaft in the same position as the cam in a breaker-point system. A permanent magnet and a coil are mounted in spaced relationship, so that the teeth of the reluctor will pass between them as the distributor shaft rotates. Each time one of the reluctor teeth passes between the magnet and the coil, the magnetic field is changed so as to alter the induced voltage in the coil. This voltage then is used to trigger the electronic ignition.
While such an approach eliminates the point wear problem entirely, it has the disadvantage that it requires total modification of the engine. In other words, such a system cannot easily be added on to an existing engine.
In contrast, it is an object of the present invention to provide an electronic ignition that can easily be added to an existing engine, and which employs the existing points as a timing control means. By eliminating the high currents normally switched by the points, point wear is substantially eliminated. Point lifetime is increased immensely, with a concomitant elimination of the misfiring and improper timing problems associated with breaker point wear.
Other objects of the present invention include (a) voltage regulation to insure consistant spark energy; (b) provision for maintaining the same spark level despite changes in battery output, such as the reduced voltage level during engine cranking; (c) point bounce elimination circuitry to insure that false firing will not occur as a result of point contact bounce; (d) means for automatically cleaning the points; and (e) automatic switchover to conventional ignition operation in the event of electronic ignition failure.